Video projection systems are widely used in a variety of applications. For example, video projection systems, both forward and rear projection systems, are widely used in “big screen” home entertainment systems to provide a much larger picture than is economically available using a conventional cathode ray tube. Additionally, video projection systems may be used in a theater to display a movie or other video program for a relatively large audience. Video projection systems are also used in business, education, training and other areas to display presentations such as, pictures, graphs, charts, outlines, a computer desktop etc., for a number of people to view. Because video projection systems are so widely used, there is a constant desire to improve on known video projection systems.
In general, a projection system is provided with a video signal bearing the image or images to be projected. A lamp produces a powerful light beam that is then directed to a micro-opto-electro-mechanical system (MOEMS) device. The MOEMS device is a light modulator that modulates incident light in a spatial pattern that corresponds to the image of the incoming video signal. Thus, the modulator is driven with the incoming video signal to produce the image to be projected. The light from the projection lamp is then passed through, or reflected from, the modulator to project the image on the modulator to a screen or other display surface.
One type of light modulator includes an array of micromirrors mounted on movable elements. Each individual micromirror can be independently deflected by an electrostatic force. Thus, when a light beam is directed onto the array of micromirrors, each of the mirrors will reflect light in varying amounts depending on the deflection and consequent orientation of that mirror. Each mirror can thus be used to represent a pixel of the image from the incoming video signal.
To produce a bright pixel, the deflection or orientation of the micromirror associated with that pixel is controlled such that the reflected light from the micromirror is directed into the projection optics of the projection system for projection. To produce a dark pixel, the deflection or orientation of the micromirror is controlled such that the reflected light from the micromirror is directed away from the projection optics. In order to display a black-and-white image, the micromirror array is illuminated by a beam of light. By coordinating the reflective status of the micromirrors based on the brightness of the pixels of the desired image, the collective effect of all reflected light from individual micromirrors is the generation of the desired image. Gray-scale and color images can also be produced using the micromirror array.
The micromirror array is a delicate device. Its performance can be significantly degraded by, for example, moisture or contaminants that may adhere to any of the micromirrors or by changes to the internal operating environment such as pressure and gas constituents. For this and other reasons, micromirror array devices need to be packaged after fabrication. For example, see U.S. Patent Application Publication No. 2004/0190112 to Huibers, Sep. 30, 2004, which is incorporated herein by reference in its entirety.